The present invention relates to an automatic bobbin thread guiding apparatus for a sewing machine, more particularly to such an apparatus for making the bobbin thread engage automatically with the bobbin thread tension adjusting mechanism in cooperation with manual shutting operation to shut the shuttle race slide from its opened position to its shut position.
Before starting of a sewing operation with a mechanical or electronically controlled sewing machine, after selecting desired needle thread and bobbin thread, an operator has to set the needle thread along the needle thread passage extending from the needle thread spool to the eye of the needle, and also has to set the bobbin in the bobbin case of the rotating shuttle and then has to make the bobbin thread engage with the needle thread at the eye of the needle after guiding the bobbin thread through the bobbin thread tension adjusting spring mechanism.
Many recent sewing machines are provided with a horizontally rotating shuttle because of simplified bobbin cases. In these sewing machines, as preparatory work, the operator has to draw out the bobbin thread through a guide slit of the bobbin case and then make the bobbin thread engage with the bobbin thread tension adjusting spring mechanism. After that, the operator has to reciprocate the needle vertically by one cycle with manual driving and then draw out the bobbin thread intersected with the needle thread end through the needle hole of the throat plate. The operator has to do this preparatory work manually. Meanwhile, various automatic needle thread engaging mechanisms for simplifying the engaging operation of the needle thread have been proposed, but the present inventor does not know of any automatic bobbin thread engaging mechanism for simplifying the engaging operation of the bobbin thread. In a sewing machine including a horizontally rotating shuttle, it seems impossible to install a bobbin thread engaging mechanism in the very narrow space between the bobbin case and the throat plate.
Additionally, Japanese Utility Model Publication (not examined) No. 55-11103 discloses a mechanical structure of a bobbin case in a horizontally rotating shuttle that can decrease noises caused in a sewing operation and wear of the bobbin case. On the other hand, Japanese Utility Model Publication (not examined) No. 55-58173 discloses a mechanical structure of a horizontally rotating shuttle that makes the bobbin thread disengage from the thread engaging portion of the adjusting plate and engage automatically with the engaging portion during a sewing operation, by means of a spring member for preventing the bobbin thread from disengaging between the adjusting plate and the tension adjusting spring of the bobbin thread tension adjusting spring mechanism.
However, these mechanisms are useless for simplifying and automating an engaging operation of the bobbin thread. As described above, in order to prepare the bobbin thread, while clamping the bobbin thread end with fingers, the operator has to introduce the bobbin thread into the guide slit and then move the bobbin thread end leftward slightly to make the bobbin thread engage with the bobbin thread tension adjusting spring mechanism. At the same time, the operator has to check whether the thread is engaging surely or not. Therefore, these engaging operations of the bobbin thread are rather complicated and troublesome for the operator. Furthermore, these engaging operations are necessary for every exchanging of the bobbin, so the operations are very difficult for unskilled operators.